This invention relates to a push button switch including a housing, a depressible plunger which is spring-urged towards a first, rest position in the housing, and a pair of cooperating blade springs each of which is fixed relative to the housing at one end and free at the other end. Each blade spring carries a respective electrical contact at the free end and has a shoulder which is engageable by a respective portion of the plunger during depression of the plunger to cause the springs to move inwardly towards each other such that the respective electrical contacts engage. The depression force required on the plunger to cause its portions to ride over the shoulders is greater than the depression force required to complete the depression once the portions have ridden over the shoulders. In such a switch, when the plunger engages and starts to move the shoulder in each blade spring, the operator feels an increased resistance to further movement, but after the switching operation has taken place this resistance decreases rapidly and the maximum depression is suddenly reached, so giving a tactile feedback.
Such a switch is known, for example, from the published United Kingdom patent application No. 7845128 (Ser. No. 2023933A), in which the free ends of the blade springs are self-tensioned apart and bear on opposing faces of a cavity or recess in the plunger.
Switches of this type are often very small, for example when used in push button telephone instruments, and the contact gap between the electrical contacts is also very small. If the push button is jolted or subjected to vibration, it is possible that the free ends of the springs may be jerked away from this rest position to such an extent that their contacts touch each other. Further, the magnitude of the tactile feel is dependent upon the self-tension in the springs, hence requiring that the tensions are accurately adjusted during manufacture. Also, the pre-tensioned springs are difficult to insert in the plunger recess during assembly.